Earth Fist

 
Prerequisite(s): Earth Sense, Improved Unarmed Strike, Con 13+, Wis 13+, Dwarf, Gnome or Goliath.
 
Benefit: As long as you are touching the ground, your unarmed attacks are treated as cold iron weapons for the purpose of dealing damage to creatures with damage reduction.
 
Special: A fighter may select Earth Fist as one of his fighter bonus feats.
 
Source: Races of Stone